Levels of pesticide residues in the blood of ortolan buntings (Emberiza hortulana), skylarks (Alauda arvensis) and yellowhammers (Emberiza citrinella) from Sweden.

Bird declines in European farmland have been linked to pesticide-driven food depletion and chronic exposure to pesticides well below levels causing acute toxicity. Yet, the extent of bird contamination by plant protection products remains largely unknown, partly because existing biomonitoring methods require relatively large blood volumes. Here, we developed a novel blood microsampling procedure (8 µl) combined with LC-MS/MS screening of 104 pesticides to determine exposure in nestling yellowhammers Emberiza citrinella (N = 5) and skylarks Alauda arvensis (N = 40) as well as adult ortolan buntings Emberiza hortulana (N = 21), species that have declined in European farmland over the last 60 years. Sampling was performed in Sweden from 2014 to 2016. Pesticide exposure was widespread: residues were detected in half of the nestlings (mean ± sd: 0.49 ± 0.07). Among individuals that tested positive for any pesticide, the mean number detected was 2.01 ± 0.49, with up to seven pesticides in a single nestling. Concentrations of individual pesticide residues in blood were relatively low compared to other studies (0.02-50 ng/ml) and were restricted to fungicides (N = 8) and herbicides (N = 5) in nestling skylarks and yellowhammers. Our results also provide the first evidence that exposure of migratory ortolan buntings to insecticide chlorpyrifos outside Sweden can be detected in the blood samples on their Swedish breeding grounds (7/10 tested positive; 0.25-0.56 ng/ml). These findings have key ecological and conservation implications, highlighting the need for and feasibility of, continued monitoring of pesticide exposure and its effects on non-target species in agro-ecosystems.